Fix pets lagging behind and despawning by slightly adjusting speed

if too far from owner.

Closes #8740

src/server/game/Entities/Unit/Unit.cpp

@@ -12690,7 +12690,22 @@ void Unit::UpdateSpeed(UnitMoveType mtype, bool forced)
         {
             // Set creature speed rate from CreatureInfo
             if (GetTypeId() == TYPEID_UNIT)
-                speed *= ToCreature()->GetCreatureTemplate()->speed_run;    // at this point, MOVE_WALK is never reached
+                if (isPet() && !isInCombat())
+                {
+                    // For every yard over 5, increase speed by 0.01
+                    //  to help prevent pet from lagging behind and despawning
+                    float dist = GetDistance(GetCharmerOrOwner());
+                    float base_rate = 1.00f; // base speed is 100% of owner speed
+                    
+                    if (dist < 5)
+                        dist = 5;
+
+                    float mult = base_rate + ((dist - 5) * 0.01f);
+
+                    speed *= GetCharmerOrOwner()->GetSpeedRate(mtype) * mult; // pets default to owner's speed when not in combat
+                }
+                else
+                    speed *= ToCreature()->GetCreatureTemplate()->speed_run;    // at this point, MOVE_WALK is never reached
 
             // Normalize speed by 191 aura SPELL_AURA_USE_NORMAL_MOVEMENT_SPEED if need
             // TODO: possible affect only on MOVE_RUN